CVTs include a belt comprising a stacked ring assembly made up of a plurality of stacked metal rings for transmitting power. The metal rings are generally manufactured by cutting a hollow cylindrical drum constituted from maraging steel into a plurality of metal rings having a prescribed width, and then holding the metal rings on a rack as disclosed in Japanese Laid-Open Patent Publication No. 2007-191788 and performing a heating treatment process on the metal rings, such as a solution treatment process, an aging treatment process, or a nitriding treatment process.
FIG. 7 is a plan view of a ring supporting device 2 for supporting metal rings 1, and for feeding and transferring the metal rings 1 onto a rack. The ring supporting device 2 is mounted on the distal end of an arm of a feed robot (not shown), which also is referred to as a loader.
The ring supporting device 2 includes a fixed base 3 and a movable base 5, which is movable toward and away from the fixed base 3 by two cylinder columns 4a, 4b. The fixed base 3 and the movable base 5, which are substantially semicircular in shape, have respective straight portions facing each other, which are disposed substantially diametrically thereacross.
The cylinder columns 4a, 4b comprise cylinders having cylinder tubes 6a, 6b coupled to the fixed base 3, and rods 7a, 7b coupled to the movable base 5. As shown in FIGS. 7 and 8, when the rods 7a, 7b are extended and retracted, the movable base 5 is moved toward and away from the fixed base 3. As shown in FIG. 9, vertical support walls 8 extend from the fixed base 3 and the movable base 5.
The feed robot first places the ring supporting device 2 shown in FIG. 7 so as to face toward the inner walls of a plurality of the metal rings 1. Then, as shown in FIG. 8, the cylinder columns 4a, 4b are actuated to bring the support walls 8 of the fixed base 3 and the movable base 5 into abutment against the inner walls of the metal rings 1. The rods 7a, 7b are extended a predetermined distance in order to cause the support walls 8 (see FIG. 9) to support the metal rings 1, as the metal rings 1 are elastically deformed into an elliptical shape. The arm of the feed robot is then operated to feed the metal rings 1 together with the ring supporting device 2 toward the rack.
After the ring supporting device 2 has placed the metal rings 1 between a plurality of holding shafts of the rack, the rods 7a, 7b are retracted. As a result, all of the metal rings 1 are returned elastically to a circular shape, and inner walls thereof are spaced from the support walls 8, while the outer walls thereof are held against the side walls of the holding shafts, whereupon transfer of the metal rings 1 onto the rack is completed.
The metal rings 1, which are fabricated as described above, are not of constant dimensions, but inevitably suffer from variations due to the manufacturing process in relation to the inside diameters, circumferential lengths, and widths thereof, as disclosed in Japanese Laid-Open Patent Publication No. 2004-122277 and Japanese Laid-Open Patent Publication No. 2002-086322. In other words, the metal rings 1, which are supported by the ring supporting device 2, may have larger and smaller inside diameters, for example.
When the metal rings 1 are simultaneously supported on the support walls 8, the rods 7a, 7b need to be extended to positions where the rods 7a, 7b are capable of supporting the metal rings 1, in order to prevent metal rings 1 having a maximum inside diameter from dropping off from the support walls 8. In this case, since it is necessary to pull the metal rings 1 having smaller inside diameters, the cylinder columns 4a, 4b need to produce large actuating forces. Thus, the metal rings 1, which are pulled in this manner, may exceed an elastic deformation range and may become plastically deformed.
Consequently, the ring supporting device according to the background art is disadvantageous, in that the ring supporting device is large in size and heavy in weight, due to the need for cylinders that produce large actuating forces, and since some of the metal rings having smaller inside diameters tend to become plastically deformed.